Acknowledgments
We thank Chris Griffiths, Pam O’Brien, Tristan Ricketson, Jess Ward-Jones, Ian Pulsford, David Freudenberger, David Berman, and Joanne Lenehan.
This document was based on the Draft Ecology and Conservation Modelling Preregistration Template by Chris Jones and Elliot Gould. We omitted a number of their proposed sections for which we had no answer at this stage - look out for their full template and follow the project at xxxx.
1. Problem Statement
1.1 Study context and Purpose
1.1.1. Key Stakeholders
This research project pre-registration proposes an investigation on the Country of the Monaro Ngarigo people, Traditional Custodians of land including the southern section of Kosciuszko National Park, NSW, Australia. The application of the concept of significant cultural values described here is informed by people who speak for that Country and their trusted contacts.
The ongoing custodianship of the Monaro Ngarigo people is acknowledged by NSW Department of Planning, Industry and Environment’s National Parks and Wildlife Service (NPWS) through a Memorandum of Understanding for joint management of the southern section of Kosciuszko National Park [1]. An earlier version of this proposal was presented to the Executive Committee representing the Aboriginal Community of the Southen Snowy Mountains (the group as named in the MoU) for consultation, and they should be encouraged to remain involved in the project should it proceed.
1.1.2 The problem, and purpose of the model
Feral herbivores pose a serious threat to Australian ecosystems and native biodiversity [2], including our species and ecological communities threatened with extinction or collapse. There is far less attention to how those herbivores may threaten significant cultural values of landscape for Aboriginal Australians.
The landscape and riverscape of the lower Snowy River Valley has by many published and anecdotal accounts been increasingly impacted by feral herbivores [3]. Recent dung counts from a set of exclosures established in the 1980s to distinguish between the impacts of rabbits and kangaroos instead tell the story of the increasing dominance of horse and deer [4]. Even after a period of drought followed by fierce wildfire, feral horse numbers in Kosciuszko National Park were estimated at 14,000 in Spring, 2020 [5]. Deer populations have also been expanding through the area and Herbivore signs are everywhere from the valley floor to the stony ridges.
This study will examine the relationship between vertebrate herbivores - feral and native - and the regeneration of kurrajong (Brachychiton populneus), a tree species that exemplifies the living connection of Monaro Ngarigo people to Country. A focus on one particular cultural value risks missing the point of the deep and encompassing spiritual connection of those people to Country as a living whole [6], but at least this particular example of a tree species may encourage readers to think of living cultural connection to landscape rather than a historical presence evoked by a focus on physical artifacts.
The kurrajong is what is referred to as a ‘culturally significant species’ (sensu [7]), an important resource providing food (seeds, new leaf buds), fibre (fish nets, string), gum, and the possibility of water in hard times whose value for Aboriginal Australians has been documented for a long time (e.g., [8]). Kurrajong is widely distributed in south-eastern Australia and is not considered at strong risk of extinction, but global scarcity is not a criterion for cultural significance [7]. For Monaro Ngarigo people kurrajong probably signified no less than food and fibre, and probably more. The canopy of large individuals provide remarkable cooler and moister conditions than the surrounding rain-shadow woodlands (authors observation), and kurrajong are reported to have been placed and encouraged in certain locations, either through translocation of seedlings, or dispersal of seed [9]. That practice may explain in part the current day distribution of large old kurrajong dotted through the lower Snowy River valley including up into the drier slopes.
In order to manage the herbivore threat to a particular value, one would ideally know the relationship between herbivore population density and the impact on that value [11]. These density-impact functions could take a range of forms (e.g., [11]] and knowing which is applicable has enormous practical implications for managers. A highly sensitive function might suggest that only reducing herbivore populations to very low density will adequately protect the value (e.g., [12] for rabbits), whereas for a relatively insensitive function, avoiding irruptive population growth is adequate. An understanding of the density-impact function therefore allows a decision-maker to design an intervention likely to achieve the required benefit with the minimum financial cost [10] and minimum destruction of herbivores. This latter point is vitally important as the removal or destruction of feral horses is controversial.
A density-impact function requires that the value that is being impacted be clearly defined. The problem that high densities of feral herbivores may pose for kurrajong is persistent failure to establish a healthy new cohort of saplings. Mature old kurrajong are venerated, but kurrajong offer useful resources from sapling age: supple fibre could be easier to extract from the bark of saplings than from older individuals, and fresh leaf buds could be easily plucked for eating from accessible low foliage. Thus, the demographic structure of kurrajong at a point in time, and evidence for the survival and growth of emerging generations (the cultural connection through the value being maintained), represent the scope of an operational definition of the value for this study.
This observational study will examine the relationship between vertebrate herbivore activity and the demographic structure and seedling survival of kurrajong in the lower Snowy River Valley. The study will be limited to locations where veteran kurrajong are found on the basis that those locations represent the most likely site where seedling establishment and progression through sapling phase to maturity would have occurred. If a strong association between herbivore activity and demographic or seedling frequency and condition is found, we will explore what levels of herbivore activity (a proxy for density) present a threat to ongoing population stability.
1.1.3 Research questions and hypotheses
Is kurrajong demographic structure related to feral herbivore activity? If feral herbivores affect demographic structure, then all else being equal, higher herbivore activity will reliably ‘predict’ sites where veteran kurrajong are accompanied by few seedlings and saplings, and those saplings will show signs of having been repeatedly browsed or damaged.
Kurrajong recruits readily from seed and is robust to transplanting at young seedling age. In some circumstances it has proved capable of prolific if not invasive recruitment under established canopy of other species e.g., [13]. Therefore seedling recruitment appears likely to be a dynamic response variable in this context.
Veteran kurrajong are to be found on the valley floor and hillslopes in the lower Snowy Valley corridor up to around 750 m altitude (Fig. 1). Considerable variation in soil depth, nutrition, and water availability is expected across that natural gradient from mild slope –> valley floor –> exposed harsh slope, and that variation would be expected to influence inherent germination and survival probabilities for kurrajong seedlings in a hypothetical herbivore free setting, and also influence herbivore activity (better resource availability promoting foraging opportunity, therefore higher activity).
Figure 2. Basic sampling concept, based around veteran kurrajong on hillslopes and the valley floor.
A main effect of sample location on kurrajong demographic structure and seedling survival is anticipated, and a main effect of herbivore activity. An interaction is expected whereby relatively less herbivore activity in lower resource locations has a disproportionately high impact on kurrajong demographic structure and seedling survival.
1.1.3 Development of response variables
One measure of interest is population demographic structure, the distribution of age classes at sampling locations, which may relate to contemporary and historic patterns of herbivore activity.
However, as each sampling unit is intended to be based on a veteran individual, and at the intended sample size, we are unlikely to observe sufficient individuals to generate robust statistics of distribution per plot.
Response variables for modelling will likely be fashioned around the density of juvenile individuals around the veteran individual. If we imagine the following classes — new seedling (first season) –> established seedling (1-2 years) –> sapling (2-5 years) –> pre-reproductive (5-\(x\) years) –> mature reproductive (\(x\)–\(y\) years) –> veteran (\(>y\) years) — we might be particularly interested in the first three categories.
Seedling density
The number of “seedlings” in a quadrat is one simple candidate response variable. However, very small plants could be newly germinated (e.g., Fig. 3 - recently germinated individual with cotyledons) or an older ‘seedling’ indicating various seasons of growth and repeated browsing (Fig. 4).